The present invention relates to a storage system and, more particularly, to a storage system configuration and a backup acquisition method based on the storage system.
Generally, if data recorded in a storage system is lost due to a hardware problem in the storage system, defective software, an erroneous operation or for some other reason, it is necessary to carry out a dump process in which data is periodically copied and stored in a backup medium for restoration of lost data, namely a backup operation is performed.
In a conventional storage system, backup software is installed in a backup server, and a user operates this backup software to issue an instruction to start the backup process. As an instruction to start the backup process is issued, the backup server reads data to be backed up (original data for backup) from the storage system and records it in a tape device. If the original volume for backup in the storage system becomes unusable due to a system problem or for some other reason, the backup data recorded in the tape device is read out so as to restore the data in a volume in the storage system, thereby to recover the condition before occurrence of the problem.
There are generally three types of backup methods: full backup where a whole volume (data) is backed up; differential backup where, with an acquired full backup as a base, a part which is not changed (updated) is not backed up and a part which is changed is backed up; and incremental backup where only a part which is changed after the time point of the previous backup, whether it is full backup or differential backup, is backed up.
In the full backup method, a whole volume is copied, and thus the volume obtained by restoration of the acquired data is complete.
In the differential backup method, it is necessary to restore full backup data first and then copy differential data acquired as changed (update) data onto the full backup to recover the data which existed at the time of backup acquisition. In the incremental backup method, it is necessary to restore full backup data first as in the differential backup method, and then copy all generations of acquired update data repeatedly.
In the differential backup method, a full backup is used as a base for data acquisition, so it is only necessary to make one copy of the full backup; on the other hand, in the incremental backup method, a backup of changes from the last acquired backup is repeated, and thus all generations of acquired differential data must be copied repeatedly. Therefore, as the number of generations or changed data blocks increases, the time required for restoration increases. The data restoration processes in the full backup, differential backup, and incremental backup methods may be applied in the present invention.
One example of a conventional technique for the backup of large volumes of data is as follows: full backup and differential backup (backup of changes after the full backup) are combined to reduce recovery processing time after backup acquisition (see JP-A No. 84728/1995). JP-A No. 84728/1995 discloses a system where either differential backup or full backup is chosen depending on the volume of update data.
Since the speed of making a backup using a tape device is low, backup takes a longer time as larger volumes of data must be handled. Besides, backup software is needed to perform backup to the disk device, and with some types or versions of an OS or some backup software currently in use, it may not be possible to perform the backup process.
The most important parameters for the backup process are Recovery Point Object and Recovery Time Object: Recovery Point Object specifies a time point up to which data should be traced back and recovered, and Recovery Time Object specifies how much time should be taken to restore data. Specific means to achieve these objects have not been provided heretofore.
The problems encountered heretofore are as follows. The user has to construct a backup system, taking into consideration the following factors: the details of a complicated storage volume structure, the performance and access frequency and so on.
In addition, because the access frequency and total size of the changed blocks, which largely vary during an operation, are difficult to predict, it is impossible to optimize the backup process. In some cases, the total size of the changed blocks is more than expected and the recovery time is much longer than expected. Furthermore, the user has to consider the complicated backup system configuration and do various troublesome tasks: selection of the backup method, backup destination capacity management, backup scheduling and so on.
According to JP-A No. 84728/1995, the amount of present update data is detected and the backup method is chosen depending on whether the amount is larger or smaller than a reference value. In this approach toward backup method selection, the recovery processing time is not taken into consideration. Although JP-A No. 84728/1995 mentions reduction in recovery processing time, this simply implies that the reading time is shortened by automatic elimination of unnecessary backup destination media.